1. Field of the Invention
The invention relates to a contact pressure element for metal foil blanks laid around the neck and top of bottles in a labelling machine, the contact pressure element being movable axially towards the end face of the bottle top and having an internally bell-shaped casing and a resiliently deformable plate, more particularly a plate which is made of a resilient foamed plastics at least on its front side adjacent to the end face of the bottle top and which is disposed in front of the opening in the casing facing the end face of the bottle and bears on the rear side against the edge of the casing.
2. Discussion of Prior Art
Foil blanks, which in a labelling machine are laid around the bottle neck and top with the tip projecting over the end face of the bottle top must, when the tip has been folded over on to such end face, be pressed as smoothly as possible against the end face and the bottle top. In a contact pressure element for this purpose known from practical work and the Patent Literature (German Patent 34 37 283 A1) the resilient plate is built up from individual discs. The rear side disc of the plate comprises a flexible but non-extensible flat material in stellar shape and is sewn at a number of places to the resilient foamed plastics plate. When the contact pressure element is lowered on to the end face of the bottle, the plate is deformed while being simultaneously forced back against a resilient bearing element, and due to the rounded surfaces of the internally bell-shaped casing the plate is forced like a hood radially also against the sides of the bottle tops. It has been found that the resilient foamed plastics front side of the plate which acts directly on the metal foil blank becomes folded more particularly when the plate has such a large diameter that it can press the foil blank not only against the top edge of the bottle top, but to below the bottle top. Such a deformation of the plate side acting directly on the foil has an unfavourable effect on the foil blank surface, which must be as smooth as possible for optical reasons. It has also been found that when the pressure is applied the foil blank is subjected to such heavy tensile stressing that damage cannot always be avoided. The stressing is high because the plate is so constructed that when the contact pressure element is lowered, the plate must slide along the inside of the bell-shaped casing to enable it to apply itself in hood shape around the bottle top.
In another similar prior art contact pressure element which, however, has proved less useful in practice than the contact pressure element having the resilient plate made up of individual discs, a foamed plastics member taking the form of a solid or hollow frustrum is disposed in a cup-shaped casing which is adapted to the shape of the foamed plastic member and against whose walls and end the foamed plastic member bears (German Patents 31 53 154 and 34 37 283). Since the foamed plastics member bears against both the walls and the end of the conical casing cup, it can yield only to a limited extent when the bottle top is introduced into the foamed plastics member, so that the latter exerts pressure laterally on the bottle top. It has been found in practice that with this method of application the foil blank is heavily loaded, so that the solid frustrum has not proved acceptable in practice. It is true that conditions are more favourable with a hollow frustrum, but the foil material still remains heavily loaded.